Hi Allon,
Thanks for your interest in Syncfusion Products.
From the code provided, it seems you were trying to change the cellvalue to 1 and then 2. I have created a sample handling this code snippet in a button1_Click() event. It works as expected. Here it was attached for your reference.
http://files.syncfusion.com/support/samples/Grid.Windows/7.3.0.20/F90247.zipIf it seems i misunderstood your requirement, please let me clear by modifying this sample implementing the requirement or issue and update.
Regards,
Rajadurai